Radio communication system



y 1945- H. w. SHERIDAN 2,375,393

RADIO COMMUNICATION SYSTEM Filed Dec. 4, 1941 INYENTOR. Iii/"am W She/Man Patented May 22, 1945 RADIO COMMUNICATION SYSTEM Hiram W. Sheridan, Oak Park, Ill. Application December 4, 1941, Serial No. 421,598

6 Claims.

This invention relates to radio communication systems and particularly to such systems for use in time. of war. During a war, ships at sea are generally forced to discontinue the use of their radio sending sets except for the sending of the most urgent messages, because enemy ships, submarines, and patrol planes are equipped with radio direction finders. With their direction finders,

they can determine the direction from which the I radio signal comes, and this assists them in locat-- ing and attacking the ship. It is thus dangerous for a ship to send radio messages with the sending set now in use, when the ship is in waters that may contain or be patrolled by enemy craft. One of the principal objects of the present invention is to provide a system of radio communication that will permit the sending of messages without betraying the location of the sending station to enemy craft.

Another object of this invention is to provide a system of radio communication that may be used on land, as well as at sea, wherever it i desirable to conceal the location of a sending station, as a sending station operated by secret agents or raiding parties in territory controlled by the enemy, or a sending station connected with an objective that the enemy might wish to bomb.

Another object of this invention is to provide a system of-radio communication that will be affected relatively little by static.

' Still another object of this invention is to provide an arrangement of antenna on an airplane that will receive signals transmitted according to my system of radio communication and that will be relatively unafiected by static discharges from the airplane.

Other objects and advantages of my invention will appear from the following description and the accompanying drawing, in which Fig. 1 is a diagram of a ship sending a signal to a friendly airplane by my novel system of radio communication;

Fig. 2 is a diagram showing the paths of radio waves sent out in accordance with my novel system;

Fig. 3 is a plan view of a portion of an airplane the magnetic lines of force accompanying or forming a part of the radio waves extend horizontally. When a loop antenna is placed in an upright plane directed towards the sending station, the magnetic lines of force out across and thread through the loop. As the radio waves pass by the loop, the number and direction of the lines of force threading through the loop changes and the changes cause currents to flow in the loop with the frequency at which the radio waves are passing by. Thus radio signals can be received by a loop so placed.

If the loop is placed so that it is face-on to the radio waves instead of edge-on, it will lie in a plane parallel to the magnetic lines of force, and none of them will thread through the loop. No signal will then be received. By swinging the loop around and determining the positions at which the signal is loudest and at which it cannot be heard, the direction from which the signal comes can be determined, and it is by this means that radio direction finders operate.

. In accordance with my invention, the radio waves are polarized, but the direction of the polarization is at right angles to that of the radio waves now used, so that the magnetic lines of force are vertical instead of horizontal. As shown in Fig. 1, a ship I0 sailing in a sea II which may contain enemy craft is provided with an antenna I2 constructed so as to send out waves whose magnetic lines of force I3,.I4, I5, l6, l1, I8, and I9 ie in vertical planes.

The antenna I2 may be formed of two horizontal halves located end to end and joined by an insulator 2| and is supported from masts 22 and 23 through end insulators 24. The two halves of the antenna I2 are connected through two leadshowing the location of an antenna for use in my create radio waves which are polarized so that 55 in wires '25 to a transmitting set located in a radio room 26, and the transmitting set isarra-nged so that the energy fed to one lead-in wire is 180 out of phase with the energy fed to the other lead-in wire. The currents in one lead-in wire will always be equal to and in the opposite direction to the current in the other, so their ma netic fields will neutralize each other. The currents in the two halves I2 of the antenna will, on

'the contrary, be in the same direction and be horizontal, creating magnetic lines of force I3, I4, I5, I6, I1, I8 and I9 in vertical planes. Actually, the lines of force I3, l4, I5, l6, I 'I, I8 and I9 will extend around the antenna I2 as an axis, but the antenna has been shown as seen from the side instead of from the end in order to make the illustration clearer. g

When the radiating magnetic lines of force I8 successively enter and leave the loop 28 and thus induce in it a radio frequency current corresponding to the signal being sent from the ship l0, and the signal is therefore received by the radio set in the airplane 21. However, this gives no indication of the direction from which the signals come, so that, if the airplane 21 should happen to be an enemy patrol bomber, it will not be able to use the signal as an aid in locating the ship l0, and the ship will not have betrayed its location by the use of its radio.

A vessel on the surface of the sea H and within a few miles of the ship Ill, such as the submarine 30 in Fig. 2, will be able to receive the signals sent out by the ship if it happens to be equipped with an antenna that will respond to radio waves whose magnetic lines of force are in vertical planes, but it will be unable to determine the direction or location of the ship 10. A vessel farther away, such as the submarine 3|, will be unable to receive any signal at all, because the radio waves sent out by the ship [2 and following a path 32 alon the surface of the sea are rapidly absorbed by the sea, which is an excellent conductor of electricity, and, by the time they reach the vessel 3|, are too weak to cause a signal in a receiving set even if the set is equipped with the proper type of antenna for receiving radio waves polarized in the manner described above.

The signals from the ship [0 can be received by the airplane 21, even if it is at a considerable distance from the ship, because the signal received by the plane travels along a path 33 which is far enough above the surface of the sea I! so that the portions of the waves travelling along this path are not absorbed by the sea. The signals from the ship ID will also be received by a distant station 34 on land because the signal received by the distant land station 34 travels along a path 35 that rises far above the surface of the sea, the portions of the waves travelling along the path 35 being bent or reflected back down to earth by the ionized Heaviside layer 36 in the upper portion of the atmosphere. distant vessel 3'! will receive the signal travelling along a path 38 extending up into the Heaviside layer, and it may receive the signalwith an ordinary antenna or loop, because the polarization of the waves may be changed by the Heaviside layer 36. However, the distant vessel 31 will not,

inany case, be able to locate the ship I0 because no accurate indication of its direction can be obtained from an obliquely polarized wave coming down obliquely from the Heaviside layer. Moreover, even if the distant vessel 31 were able to determine accurately the direction of the ship II], it is too far away to-make effective use of the information.

My system of radio communication has been described above as used for sending signals from a ship to an airplane and to a short station, but this is only by way of example. Obviously, it may Similarly, a

be used in many cases-between ships, land stations, aircraft, or mobile land stations.

Besides the relative secrecy which it provides, my system of communication has a particular value when used in sending signals to aircraft, because it permits the use of an arrangement of loop antenna that is relatively free from static. When a loop antenna is used, my system requires that the loop be placed in a horizontal plane in order to secure the maximum strength of signal.

.When the loop is placed on an airplane, as shown in Fig. 1, the loop 28 may be placed on the airplane 21 in such a position that it is not affected by much of the static to which conventional loops are sensitive. As shown on a larger scale in Figs. 3 to 5, the loop 28 is enclosed in a flat streamline metal casing 41 and is supported in a horizontal plane directly above the center of the wing 48 of the airplane 21 by means of streamline supports 42. The loop 28, as may be seen from the drawing, is thus directly above both the axis or center-line 43 of the fuselage 44 and the axis or mid-chord-line .45 of the wing 46, and a perpendicular to the plane of the loop 28 at its center will pass through both of these lines. The advantage of this location will be explained below.

As is well known, a loop antenna is affected by the moving magnetic field which accompanies a radio wave and it is affected by only those fields in which the lines of force pass through the loop. Therefore, when the loop 28 is mounted horizontally as shown, it will be affected only by radio waves or electrical disturbances whose magnetic fields are vertically polarized.

The ordinary static heard during thunder storms is caused by the radiating electromagnetic field caused by a stroke of lightning. Since most lightning consists of an electrical discharge traveling in a vertical or approximately vertical path, the lines of magnetic force radiated by the discharge will lie in horizontal or approximately horizontal planes. These radiating lines of force and the accompanying electrostatic lines of force constitute the ordinary form of static but, since the lines of magnetic force are approximately .horizontal, they will not thread through the horizontal loop 28, and cause little or no effect on it.

Thus, the static will not affect the receiver conother, or at the tail of the airplane because electrostatic charges tend to concentrate near 'the ends of elongated bodies. If the discharge takes place from one wing tip, a momentar current 41 is created extending lengthwise of the wing, and it is the magnetic field accompanying this current which affects the ordinary airplane antenna and is heard as static in the radio. When the loop antenna 28 is placed horizontally above the center of the wing, as shown in the drawings, the magnetic lines of force 48 accompanying the longitudinal current 41 in the wing 48 do not thread through the loop 28 and have no effect, on it. Therefore, the static discharge is not heard in the radio set connected to the loop.

Similarly, when the static discharge takes place at the tail or nose of the airplane, a momentary current 49 extending longitudinally of the fuselage 44 is set up. The lines of force 50 of the magnetic field accompanying this current will not thread the horizontal loop 28 and thus this type of discharge will not be heard as static in the receiver connected to the loop.

The streamlined metal housing 4| enclosing the loop 28 is grounded to the fuselage 44 so that there will be no accumulation of static electricity on the loop itself, and the housing 4| is provided with a radial slot 5| in order that it will not prevent the loop from receiving signals. The loop antenna 28 is shown in Figs. 3 to 5 as installed on a large flying boat 2?, but it is obvious that changes may be made to suit different airplanes. For example, on a large land plane, the loop might be placed below the fuselage instead of above.

From the above description, it will be apparent that I have provided not only a relatively secret system of radio communication that is particularly useful in time of war, but also a system of radio communication for airplanes that is relatively free from interference from static.

While I have shown certain specific embodiments of my invention, it will, of course, be understood that the invention is not limited to these particular embodiments but may be carried out in other ways which may suggest themselves to the skilled radio engineer having the benefit of this disclosure. My invention, therefore, is not limited to the specific disclosure herein but includes all constructions falling within the terms of the following claims.

I claim as my invention:

1. In an airplane having an electrically conducting fuselage and wing, a loop antenna located outside of but closely adjacent to said fuselage and wing and in a plane parallel to the axis of said fuselage and to the axis of said wing and vertically above the intersection of the axes of said fuselage and wine.

2. In an airplane having an electrically conducting fuselage and wing, a loop antenna located outside of said fuselage and wing and in a plane parallel to the axis of said fuselage and to the axis of said wing, the center of said loop antenna being substantially in alignment with the vertical line intersecting said axes.

3. In an airplane having a substantially horizontally extending electrically conducting fuselage and an electrically conducting transversely extending wing, a loop antenna lying in a substantially horizontal plane with the vertical line that passes through the axes of said wing and fuselage extending through said loop.

4. In an airplane having an electrically conducting wing and an electrically conducting fuselage, a radio receiving loop located parallel to the lines of electro-magnetic force set up by a longitudinal oscillatory current in the wing and parallel to the lines of electro-magnetic force set up by a longitudinal oscillatory current in the fuselage, said loop being so located above the axes of said wing and fuselage as not to be affected by magnetic lines of force caused by currents of electricit flowing along said wing or fuselage.

5. A system for providing radio communication to an airplane comprising a sending station having an antenna oriented to send out radio waves with magnetic lines of force in vertical planes and a loop antenna on the airplane, the loop antenna lying in a horizontal plane with the vertical axis thereof passing substantially through the longitudinal axis of the fuselage of the airplane and substantially through a line midway between the leading and trailing edges of the wings of the airplane said fuselage and wing being electrically conducting, whereby static caused by discharges from the airplane itself to the surrounding atmosphere will not be audible in the receiver.

6. In an airplane having an electrically conducting fuselage, an electrically conducting wing extending transversely to said fuselage, a loop antenna located outside of the fuselage and in close proximity thereto ,and lying in a horizontal plane substantially parallel to the axis of the fuselage, said loop extending about the line of intersection of planes passing through said wing and fuselage, and an annular metal housing for containing said loop, said housing having a radial slot therein.

HIRAM W. SHERIDAN. 

